Heater not acting right, basically seems the heat control knob has no affect on heating temp seems to be full hot, or if I turn to 65 the AC will kick on. So whatever "door" seems to work but what should be adjustable heat is not adjustable just max heat. Fan works good. Any ideas appreciated.

Does the air get cold if you turn to 65F? Can you active the self test on the temperature controls unit?
The heater blend door actuator is a known problem on these older Nissans.

fontana dan wrote: ↑

Sun Feb 26, 2023 7:28 pm

Does the air get cold if you turn to 65F? Can you active the self test on the temperature controls unit?
The heater blend door actuator is a known problem on these older Nissans.

Sorry forgot, 02 QX4. Yep gets cold if set to 65, not sure how cold but yes. Self test? Erm, would love to know how to do that- I'll check the fsm.

Wow that's quite complex. I think it's failing a sensor check will repeat. Thanks

Yep fault 22 (in-vehicle sensor) and 25 (sunload sensor). Seems the sunload sensor can be triggered by being tested in the dark, but even if the in-vehicle sensor was bad, seems that wouldn't make it so that the temp selector knob would have no affect on temp, in manual mode. I know where there's a couple of the in-v sensors, and a temp sel knob panel but... if the knob works to go thru the self test workflow, should be good? Oh well there's a very detailed diagnosis procedure, just need to dig into it.

Cool. That is helpful. The knob is working if you are able to change the temperature setting and navigate the self-test. Make sure the sunload sensor is receiving direct sunlight during the test.
Either of those sensors (in-vehicle/sunload) could cause this problem. Refer to the service manual Heating and Air Conditioning pages 131-136 for info on diagnosing this.
https://www.nicoclub.com/service-manual ... 2%2FHA.pdf
Check for 5v on pin #1 on connector for sunload sensor. There could be a circuit issue. Possibly a rodent had a snack on the wires under the dash.

fontana dan wrote: ↑

Sun Feb 26, 2023 10:18 pm

Check for 5v on pin #1 on connector for sunload sensor. There could be a circuit issue. Possibly a rodent had a snack on the wires under the dash.

+1, but check across the pins at the connector as well as to chassis ground. Both sensors are balance resistors pulling down on fixed pullup resistors in the HVAC, so seeing 5V across the pins is just as important as seeing 5V to the chassis. If you see the latter but not the former, the ground wire is broken.

Thanks all for the replies, the connector was erm, disconnected. I'm sure I had absolutely nothing to do with that- ha. Working great now.